In several situations it is necessary to cut a narrow deep channel, or kerf, for example, when cutting rocks in granite, marble and other rock quarries. Kerfing may also be used in cutting rock tunnels for highways and in mining, among other applications.
The current method of deep kerfing in rocks has been to use either rotating or oscillating water jets. In order for a water jet to cut rock, the stagnation pressure of the water jet must exceed the threshold pressure of the rock, a concept that has been well documented in literature regarding water jets. As an example, granite can have a high threshold pressure such that water jets having pressures of 35,000 psi and beyond are needed to cut the rock. Current systems reaching these pressures typically have round jets with a diameter on the order of 0.01 to 0.080 inch. While the nozzle that holds such jets is typically much larger than the jet diameter, the width of the kerf that is cut closely corresponds to the jet diameter. This creates several problems. In order to cut a kerf to a given depth, it is necessary to move the nozzle closer to the bottom of the kerf to maintain a strong jet. However, because the nozzle is wider than the kerf that is normally formed by a jet, it is necessary to make the kerf wider than the nozzle.
In order to make the kerf wider than the nozzle, current systems typically use a rotating or oscillating water jet system. However, these systems have many disadvantages. For example, a rotating water jet system is mechanically complex and bulky in that it requires an ultrahigh pressure swivel for conveying water to a rotating stem and nozzle, and a drive system that can overcome the torque of the swivel at high pressures and rotate the stem leading to the nozzle at a required RPM. Such a system typically requires hydraulics which in turn requires pressure and return line hoses, which further complicate the system. As an example, when cutting a rock tunnel it is impossible to place the jet nozzle at a true boundary of the tunnel due to the bulkiness of current systems. It is therefore necessary to cut outwards and excavate a larger tunnel than desired so that as the tunnel is cut in steps, the nozzle can be placed at a true, desired boundary. Such a process is both time and cost ineffective.
Although an oscillating water jet system is somewhat more simple than a rotating water jet system, in that it does not require a swivel, it must still be able to convey water from a fixed conduit to a moving conduit. As a result, various fatigue problems are encountered. In addition, a drive system is still required to oscillate the assembly.
A need therefore exists for a simplified system that can cut deep kerfs in rocks while avoiding the numerous problems discussed above.